Exhaust purification device for engine

Abstract

The present invention provides an exhaust purification device for an engine, comprising: an ammonia supply system including an ammonia supply injector for supplying ammonia to a combustion chamber and a control unit for controlling the ammonia supply injector, and a NOx purification system provided in an exhaust passage and including a Selective Catalytic Reduction catalyst being able to fulfill a function for purifying NOx under the presence of the ammonia.

What is claimed is: 
     
       1. An exhaust purification device for an engine, comprising:
 an ammonia supply system including an ammonia supply injector for supplying ammonia or a substance producing ammonia to a combustion chamber, and a control unit for controlling the ammonia supply injector; and 
 an NOx purification system for purifying NOx included in an exhaust gas, the NOx purification system including a selective catalytic reduction catalyst fulfilling a function for purifying NOx under the presence of ammonia, and an exhaust-system ammonia supply system supplying ammonia or a substance producing ammonia to an exhaust passage upstream of an exhaust passage section in which the selective catalytic reduction catalyst is arranged, wherein 
 the ammonia supply system supplies the ammonia or the substance producing the ammonia to the combustion chamber in such a manner that a ratio between an NO component and an NO 2  component in the exhaust gas arriving at the exhaust passage section in which the selective catalytic reduction catalyst is arranged is made to a required ratio, during a period set according to the required ratio. 
 
     
     
       2. The exhaust purification device for the engine according to  claim 1 , wherein
 the control unit controls the ammonia supply injector to supply the ammonia or the substance producing the ammonia to the combustion chamber when a temperature in the combustion chamber is a temperature within a first predetermined temperature range. 
 
     
     
       3. The exhaust purification device for the engine according to  claim 2 , wherein
 the ammonia supply system supplies the ammonia or the substance producing the ammonia to the combustion chamber when a temperature in the combustion chamber is within the first predetermined temperature range in such a manner as to increase a ratio of NO 2  in the exhaust gas emitted from the combustion chamber to the exhaust passage by the supply of the ammonia or the substance producing the ammonia to the combustion chamber. 
 
     
     
       4. The exhaust purification device for the engine according to  claim 2 , wherein
 the first predetermined temperature range is a temperature range from 1000K to 1400 K inclusive. 
 
     
     
       5. The exhaust purification device for the engine according to  claim 2 , wherein
 the ammonia supply system includes a temperature detector for detecting a temperature in the combustion chamber. 
 
     
     
       6. The exhaust purification device for the engine according to  claim 5 , wherein
 the temperature detector includes a sensor for detecting a pressure in the combustion chamber. 
 
     
     
       7. The exhaust purification device for the engine according to  claim 2 , wherein
 the control unit controls the ammonia supply injector to supply the ammonia or the substance producing the ammonia to the combustion chamber when a temperature of the selective catalytic reduction catalyst is a temperature within a second predetermined temperature range. 
 
     
     
       8. The exhaust purification device for the engine according to  claim 7 , wherein
 the second predetermined temperature range is a temperature range from 150° C. to 300° C. inclusive. 
 
     
     
       9. The exhaust purification device for the engine according to  claim 1 , wherein
 the control unit controls injection from the ammonia supply injector in such a manner that the ratio between the NO component and the NO 2  component in the exhaust gas arriving at the exhaust passage section in which the selective catalytic reduction catalyst is arranged is made to 1:1. 
 
     
     
       10. The exhaust purification device for the engine according to  claim 1 , further comprising
 at least one of a downstream temperature detector for detecting a temperature in an exhaust passage downstream of the exhaust passage section in which the selective catalytic reduction catalyst is arranged, and an NOx detector for detecting a NOx concentration in the exhaust passage downstream of the exhaust passage section in which the selective catalytic reduction catalyst is arranged, wherein 
 the control unit controls injection from the ammonia supply injector by using at least one of the downstream temperature detector and the NOx detector. 
 
     
     
       11. The exhaust purification device for the engine according to  claim 1 , wherein
 a catalyst including no catalyst component promoting a reaction of nitrogen oxides including NO and NO 2  is arranged in an exhaust passage upstream of the exhaust passage section in which the selective catalytic reduction catalyst is arranged. 
 
     
     
       12. The exhaust purification device for the engine according to  claim 1 , wherein
 the ammonia supply system and the NOx purification system share a common tank for storing ammonia. 
 
     
     
       13. The exhaust purification device for the engine according to  claim 1 , wherein
 the ammonia supply system and the NOx purification system share a common tank for storing aqueous urea. 
 
     
     
       14. An engine, comprising the exhaust purification device for the engine according to  claim 1 . 
     
     
       15. An exhaust purification method for an engine in the exhaust purification device for the engine according to  claim 1 , comprising:
 a step of determining whether or not a temperature of the selective catalytic reduction catalyst is within an active temperature range of the selective catalytic reduction catalyst; and 
 a step of, when it is determined by the step that the temperature of the selective catalytic reduction catalyst is within the active temperature range, supplying ammonia to the combustion chamber by the ammonia supply system when a temperature in the combustion chamber is a temperature within a predetermined temperature range.